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Calculate specific energy easily with our online Specific Energy Calculator. Quick, accurate results using the formula e = E/m with unit conversions.
If you’ve ever wondered “how do I calculate specific energy?”, you’re in the right place. We developed this Specific Energy Calculator so you’ll find quick, clear answers. In this article we’ll walk you through the key formula, show how to use it, and make it easy to understand, even if you’re not a physics expert.
“Specific energy” means the energy contained per unit mass of a substance. In other words, it tells you how much energy one kilogram (or one gram) holds. This concept matters in batteries, fuels, rockets and any system where weight counts.
In everyday words: if you want a light object that packs a lot of energy for its weight, you look for high specific energy. For example, a fuel that releases a lot of energy but weighs very little has high specific energy.
The formula you’ll use is straightforward:
e = E / m
Where:
So if you know the energy in joules and the mass in kilograms, you simply divide energy by mass to get joules per kilogram (J/kg).
That equation works across many units. Just make sure you use consistent units for energy and mass, then convert to the unit you want for specific energy (like kJ/kg, Wh/kg, etc).
Here is how you use it in three simple steps:
For example: Suppose you have a battery that stores 36,000 kJ of energy and it weighs 2 kg.
Convert: 36,000 kJ = 36,000 × 1,000 = 36,000,000 J.
Mass = 2 kg.
Then e = 36,000,000 J ÷ 2 kg = 18,000,000 J/kg.
You could then convert that to e.g. kJ/kg by dividing by 1,000 → 18,000 kJ/kg.
Our calculator does all these unit conversions behind the scenes, so you just enter the numbers and pick your units.
You’ll like this tool because:
In short: whether you’re comparing battery chemistries, fuel types or engine systems, you’ll have a clear, consistent number to compare.
If you want a quick, clean way to find specific energy, you’ve found it. Remember the core formula e = E / m, pick consistent units, and you’ll get the right answer. Our calculator guides you through conversion and lets you see results in your preferred unit. Whether you’re an engineer, student or a curious learner, this tool makes a potentially tricky calculation simple.
The standard SI unit is joules per kilogram (J/kg). But you can also use kJ/kg, Wh/kg, kcal/g or BTU/lb depending on your context.
No. Specific energy is energy per unit mass. Energy density is energy per unit volume. They’re related but different.
Absolutely. Many battery specs list Wh/kg (watt-hours per kilogram). That is a form of specific energy. The higher the number, the more energy per unit mass.
Then you can reverse the formula: E = e × m. Use the specific energy (e) times the mass (m) to get energy (E).
Because mixing units (like J with grams or Wh with kg) will give wrong results. The conversions ensure all quantities are in coherent units before applying the formula.